1. Field of the Invention
This invention relates to centrifugal contactors, and more specifically, this invention relates to more efficient topographies of miniaturized centrifugal contactors realized with 3D printing.
2. Background of the Invention
Separation of liquids can be done in a variety of ways. If the liquids are immiscible and one liquid is denser than the other, centrifugal separation is a relatively quick and simple way to mix and separate the liquids. For example, water and oil are immiscible, and water is more dense than oil. Thus, after mixing, the water and oil can be separated using a device, such as an annular centrifugal contactor.
Annular centrifugal contactors spin liquids within its rotor at a high rate to impart centrifugal forces on the liquids. Centrifugal force is inertial in nature such that for different density objects rotating in the same reference frame and at the same rate, denser objects will experience greater outward force. For example, when separating an oil-water mixture, the water will experience a greater outward force, and a separation gradient will develop between the water and oil. Using this separation gradient, the water and oil can be selectively removed from the contactor. Such technology is used to recover crude oil from sea water after oil spills.
Another application for annular centrifugal contactors and immiscible liquids is solvent extraction (a type of liquid-liquid extraction). Solvent extraction processes isolate a desired compound or compounds from a feed solution (the solution comprising the desired compound dissolved in a solvent) by mixing the solution with a second immiscible liquid and then separating the two liquids. The second liquid is chosen for the desired compound's stronger affinity for that liquid over the original solvent. Depending on the polarity of the original feed solvent, the second liquid is either a polar (e.g., aqueous) liquid, such as an acid, or a nonpolar (i.e. nonaqueous or organic) liquid. Therefore, mixing the two liquids will allow the desired compound to transfer across the phase interface into the other liquid, while undesired compounds remain in the original liquid. Upon separation, the desired compound will be isolated in one of the immiscible liquids.
Separations chemistry has always played a crucial role in the preparation of reactor fuels for both nuclear energy and nuclear weapons production. It provides a means for cleaning up decommissioned nuclear facilities and disposing of high-level radioactive wastes. One strategy for reducing the volume of radioactive wastes requiring burial in geological repository is to transmute (or fission) the actinides into shorter-lived nuclides in a nuclear reactor or by bombardment with accelerator-produced neutrons. Typical fission yields for the actinides include significant amounts of the lanthanides. Some of the lanthanides have high neutron absorption cross sections, which interfere with neutron absorption and reduce the efficiency of the transmutation process. Efficient separation of the lanthanides from actinides is therefore critical to assure as low volume of waste is generated for ultimate disposal.
Separation of lanthanides from light actinides (thorium, uranium, plutonium and neptunium) are achieved by exploiting the greater extractability of the higher oxidation state of the light 5f elements (La, Ce, Pr, Nd, b Pm, Sm, Eu and Gd). However, the transplutonium actinides do not have stable higher oxidation states such that separation of lanthanide fission products from transplutonium actinides must depend on the small differences in their solution chemistry in the trivalent oxidation state. These small differences are rarely exploited when large volumes of waste are being processed using standard separators.
Among the most difficult of separations of metal ions are the intra- and inter-group separations of lanthanides and trivalent actinides. Yet, environmental concerns related to radioactivity and new high-tech developments which have increased the demand for pure lanthanides have combined to foster a greater need for effective procedure to attain these separations. Separation methods developed over the past 50-60 years are still in use.
Solvent extraction facilitates separation of lanthanides and actinides and also recovery of uranium and transuranics from nuclear waste. Some solvent extraction processes are done in a centrifugal contactor. Such a contactor comprises a rotor enclosed in a housing. Rotors require precision machining for proper balancing and tight tolerances of weir diameters. Certain housing components can be cast. (Machining requires multiple subparts, welding/brazing and additional machining.)
Centrifugal contactors must often be over-designed, incorporating excessive safety factors to handle used nuclear fuel, and also to accommodate uncertain liquid separation protocols. As such, these extremely expensive systems cannot be optimized for any particular separation.
State of the art annular centrifugal contactors are only able to extract elements that have fast kinetics, i.e., elements that will quickly transfer between the aqueous and non-aqueous (organic) phase. Fast kinetics is required because state of the art annular centrifugal contactors can only mix and hold the liquids for short residence times, typically in the range of three to five seconds for high-throughput contactors at nominal operating conditions. For most applications, the short residence time is seen as a benefit because longer residence times can cause solution degradation. For example, when reprocessing radioactive waste, solution degradation can result from irradiation of the solution. Additionally, strong acids are often used in solvent extractions, and acids can degrade the organic phase.
Notwithstanding the foregoing, short residence times are unsuitable for kinetically challenged separations that may require up to thirty seconds or more of residence time for the desired compounds to transfer between liquid phases. For example, kinetic limitations require approximately 30 seconds mixing residence time for efficient stripping (back extraction) of actinides.
Thus, a need exits in the art for an optimized system and method for centrifugal mixing having increased residence times (e.g., up to 60 seconds) such that solvent extraction processes can be performed in extraction systems targeting solutes with slow liquid-liquid interfacial transfer kinetics. The system and method should decrease droplet size while not exceeding the separative capacity of rotors. The system and method should provide steady feed flows inasmuch as low flows can degrade hold-up and mixing quality, therefor impacting consistency of inter-stage flows when multi-stage systems and methods are employed.